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Jun 29, 2018
06/18

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Jonas Braun; Hans-Werner Hammer

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We exploit the separation of scales in weakly-bound nuclei to compute E2 transitions and electric form factors in a Halo EFT framework. The relevant degrees of freedom are the core and the halo neutron. The EFT expansion is carried out in powers of $R_{core}/R_{halo}$, where $R_{core}$ and $R_{halo}$ denote the length scales of the core and halo, respectively. We include the strong $s$-wave and $d$-wave interactions by introducing dimer fields. The dimer propagators are regulated by employing...

Topic: Nuclear Theory

Source: http://arxiv.org/abs/1612.07689

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Jun 27, 2018
06/18

by
P. Niemann; H. -W. Hammer

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We investigate renormalization group limit cycles within the similarity renormalization group (SRG) and discuss their signatures in the evolved interaction. A quantitative method to detect limit cycles in the interaction and to extract their period is proposed. Several SRG generators are compared regarding their suitability for this purpose. As a test case, we consider the limit cycle of the inverse square potential.

Topics: Nuclear Theory, Quantum Physics

Source: http://arxiv.org/abs/1504.04511

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Jun 30, 2018
06/18

by
Sebastian König; Harald W. Grießhammer; H. -W. Hammer

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We provide a detailed discussion of the low-energy proton-deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels. Extending and amending our previous work on the subject, we calculate the 3He-3H binding energy difference both perturbatively (using properly normalized trinucleon wave functions) and non-perturbatively by resumming all O(alpha) Coulomb diagrams in the doublet channel. Our nonperturbative result agrees well with a...

Topic: Nuclear Theory

Source: http://arxiv.org/abs/1405.7961

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Jun 28, 2018
06/18

by
Emil Ryberg; Christian Forssén; H. -W. Hammer; Lucas Platter

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We analyze the effects of finite-range corrections in halo effective field theory for S-wave proton halo nuclei. We calculate the charge radius to next-to-leading order and the astrophysical S-factor for low-energy proton capture to fifth order in the low-energy expansion. As an application, we confront our results with experimental data for the S-factor for proton capture on Oxygen-16 into the excited $1/2^+$ state of Fluorine-17. Our low-energy theory is characterized by a systematic...

Topic: Nuclear Theory

Source: http://arxiv.org/abs/1507.08675

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Jun 30, 2018
06/18

by
Emil Ryberg; Christian Forssén; H. -W. Hammer; Lucas Platter

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In this paper, we point out that a measurement of the charge radius of Boron-8 provides indirect access to the S-factor for radiative proton capture on Beryllium-7 at low energies. We use leading-order halo effective field theory to explore this correlation and we give a relation between the charge radius and the S-factor. Furthermore, we present important technical aspects relevant to the renormalization of pointlike P-wave interactions in the presence of a repulsive Coulomb interaction.

Topic: Nuclear Theory

Source: http://arxiv.org/abs/1406.6908

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Jun 28, 2018
06/18

by
Sebastian König; Harald W. Grießhammer; H. -W. Hammer; U. van Kolck

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We present a new perturbative expansion for pionless effective field theory with Coulomb interactions in which at leading order the spin-singlet nucleon-nucleon channels are taken in the unitarity limit. Presenting results up to next-to-leading order for the Phillips line and the neutron-deuteron doublet-channel phase shift, we find that a perturbative expansion in the inverse 1S0 scattering lengths converges rapidly. Using a new systematic treatment of the proton-proton sector that isolates...

Topic: Nuclear Theory

Source: http://arxiv.org/abs/1508.05085

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Jun 30, 2018
06/18

by
H. W. Hammer; Sebastian König

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We investigate the sensitivity of the three-nucleon system to changes in the neutron-neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the the triton-3He binding energy difference and neutron-deuteron elastic scattering. Due to the appearance of an electromagnetic three-body counterterm at this order, the triton-3He binding energy difference remains consistent with the experimental value even for large positive neutron-neutron scattering...

Topics: High Energy Physics - Phenomenology, Nuclear Theory

Source: http://arxiv.org/abs/1406.1359

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Jun 30, 2018
06/18

by
H. -W. Hammer; C. Ji; D. R. Phillips

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Nuclear halos emerge as new degrees of freedom near the neutron and proton driplines. They consist of a core and one or a few nucleons which spend most of their time in the classically-forbidden region outside the range of the interaction. Individual nucleons inside the core are thus unresolved in the halo configuration, and the low-energy effective interactions are short-range forces between the core and the valence nucleons. Similar phenomena occur in clusters of $^4$He atoms, cold atomic...

Topics: Nuclear Theory, Nuclear Experiment

Source: http://arxiv.org/abs/1702.08605

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Jun 30, 2018
06/18

by
A. G. Volosniev; H. -W. Hammer

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We discuss ground state properties of a one-dimensional bosonic system dopped with an impurity (the so-called Bose polaron problem). By assumption, the boson-boson interactions are weak, allowing us to employ the mean field approximation. We calculate analytically the thermodynamic properties of this system for any boson-impurity interaction strength at zero temperature. Our approach is validated by comparing to exact quantum Monte Carlo calculations. In addition, we test it for finite size...

Topics: Nuclear Theory, Quantum Gases, Condensed Matter

Source: http://arxiv.org/abs/1704.00622

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Jun 29, 2018
06/18

by
Christiane H. Schmickler; Hans-Werner Hammer; Emiko Hiyama

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The Efimov effect in heteronuclear cold atomic systems is experimentally more easily accessible than the Efimov effect for identical atoms, because of the potentially smaller scaling factor. We focus on the case of two or three heavy identical bosons and another atom. The former case was recently observed in a mixture of 133Cs and 6Li atoms. We employ the Gaussian Expansion Method as developed by Hiyama, Kino et al.. This is a variational method that uses Gaussians that are distributed...

Topics: Condensed Matter, Quantum Gases, Nuclear Theory

Source: http://arxiv.org/abs/1612.05738

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Jun 28, 2018
06/18

by
A. G. Volosniev; H. -W. Hammer; N. T. Zinner

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In this paper, we provide a theoretical analysis of strongly interacting quantum systems confined by a time-dependent external potential in one spatial dimension. We show that such systems can be used to simulate spin chains described by Heisenberg Hamiltonians in which the exchange coupling constants can be manipulated by time-dependent driving of the shape of the external confinement. As illustrative examples, we consider a harmonic trapping potential with a variable frequency and an infinite...

Topics: Nuclear Theory, Quantum Gases, Condensed Matter

Source: http://arxiv.org/abs/1507.00186

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Jun 28, 2018
06/18

by
M. Ebert; A. Volosniev; H. -W. Hammer

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We analyze the dynamics of two atoms with a short-ranged pair interaction in a one-dimensional harmonic trap with time-dependent frequency. Our analysis is focused on two representative cases: (i) a sudden change of the trapping frequency from one value to another, and (ii) a periodic trapping frequency. In case (i), the dynamics of the interacting and the corresponding non-interacting systems turn out to be similar. In the second case, however, the interacting system can behave quite...

Topics: Quantum Physics, Quantum Gases, Nuclear Theory, Condensed Matter

Source: http://arxiv.org/abs/1512.06628

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Jun 26, 2018
06/18

by
A. G. Volosniev; H. -W. Hammer; N. T. Zinner

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We investigate the behavior of a harmonically trapped system consisting of an impurity in a dilute ideal Bose gas after the boson-impurity interaction is suddenly switched on. As theoretical framework, we use a field theory approach in the space-time domain within the T-matrix approximation. We establish the form of the corresponding T-matrix and address the dynamical properties of the system. As a numerical application, we consider a simple system of a weakly interacting impurity in one...

Topics: Quantum Gases, Quantum Physics, Condensed Matter, Nuclear Theory

Source: http://arxiv.org/abs/1502.05300

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Jun 30, 2018
06/18

by
Shahin Bour; Dean Lee; H. -W. Hammer; Ulf-G. Meißner

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We investigate the attractive Fermi polaron problem in two dimensions using non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. As a benchmark of the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find...

Topics: Quantum Gases, High Energy Physics - Lattice, Nuclear Theory, Condensed Matter

Source: http://arxiv.org/abs/1412.8175

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Jun 27, 2018
06/18

by
I. T. Lorenz; H. -W. Hammer; U. -G. Meißner

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In the most recent measurements of the reaction $e^+e^- \rightarrow p\bar{p}$ by the BABAR collaboration, new structures have been found with unknown origin. We examine a possible relation of the most distinct peak to the recently observed $\Phi(2170)$. Alternatively, we analyse possible explanations due to the nucleon$\,\bar{\Delta}$ and $\Delta\bar{\Delta}$ thresholds. The latter could explain a periodicity found in the data.

Topics: High Energy Physics - Phenomenology, Nuclear Theory, High Energy Physics - Experiment

Source: http://arxiv.org/abs/1506.02282

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Jun 30, 2018
06/18

by
I. T. Lorenz; Ulf-G. Meißner; H. -W. Hammer; Y. -B. Dong

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We calculate the two-photon exchange corrections to electron-proton scattering with nucleon and $\Delta$ intermediate states. The results show a dependence on the elastic nucleon and nucleon-$\Delta$-transition form factors used as input which leads to significant changes compared to previous calculations. We discuss the relevance of these corrections and apply them to the most recent and precise data set and world data from electron-proton scattering. Using this, we show how the form factor...

Topics: High Energy Physics - Phenomenology, Nuclear Theory, High Energy Physics - Experiment

Source: http://arxiv.org/abs/1411.1704

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Jun 29, 2018
06/18

by
P. Klos; J. E. Lynn; I. Tews; S. Gandolfi; A. Gezerlis; H. -W. Hammer; M. Hoferichter; A. Schwenk

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Ab initio calculations provide direct access to the properties of pure neutron systems that are challenging to study experimentally. In addition to their importance for fundamental physics, their properties are required as input for effective field theories of the strong interaction. In this work, we perform auxiliary-field diffusion Monte Carlo calculations of the ground and first excited state of two neutrons in a finite box, considering a simple contact potential as well as chiral effective...

Topics: High Energy Physics - Phenomenology, High Energy Physics - Lattice, Nuclear Theory

Source: http://arxiv.org/abs/1604.01387

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Jun 29, 2018
06/18

by
I. K. Hammer; C. Hanhart; A. V. Nefediev

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We investigate the effect of meson loops on the spectrum of quark states. We demonstrate that in general quark states do not tend to get very broad if their coupling to the continuum increases, but instead they decouple from the latter in the large coupling limit. We ascribe this effect to the essentially nonperturbative unitarization procedure involved. In the meantime, some quark resonances behave very differently and demonstrate collectivity in the sense that their pole trajectories span a...

Topics: Nuclear Theory, High Energy Physics - Phenomenology, High Energy Physics - Lattice, High Energy...

Source: http://arxiv.org/abs/1607.06971

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Jun 29, 2018
06/18

by
M. Hoferichter; B. Kubis; J. Ruiz de Elvira; H. -W. Hammer; U. -G. Meißner

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We present an improved determination of the $\pi\pi$ continuum contribution to the isovector spectral functions of the nucleon electromagnetic form factors. Our analysis includes the most up-to-date results for the $\pi\pi\to\bar N N$ partial waves extracted from Roy-Steiner equations, consistent input for the pion vector form factor, and a thorough discussion of isospin-violating effects and uncertainty estimates. As an application, we consider the $\pi\pi$ contribution to the isovector...

Topics: High Energy Physics - Lattice, Nuclear Theory, Atomic Physics, High Energy Physics - Phenomenology,...

Source: http://arxiv.org/abs/1609.06722

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Jun 26, 2018
06/18

by
V. Baru; E. Epelbaum; A. A. Filin; Feng-Kun Guo; H. -W. Hammer; C. Hanhart; Ulf-G. Meißner; A. V. Nefediev

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In a recent paper Phys.Rev.Lett. 111, 042002 (2013) (arXiv:1304.0846), the charmonium state X(3872) is studied in the framework of an effective field theory. In that work it is claimed that (i) the one-pion exchange (OPE) alone provides sufficient binding to produce the X as a shallow bound state at the $D^0\bar{D}^{*0}$ threshold, (ii) short-range dynamics (described by a contact interaction) provides only moderate corrections to the OPE, and (iii) the X-pole disappears as the pion mass is...

Topics: Nuclear Theory, High Energy Physics - Experiment, High Energy Physics - Lattice, High Energy...

Source: http://arxiv.org/abs/1501.02924